Siboglinidae

Siboglinidae, also known as the beard worms, is a family of polychaeteannelid worms whose members made up the former phylaPogonophora (the giant tube worms) and Vestimentifera.[1][2] They are composed of about 100 species of vermiform creatures and live in thin tubes buried in sediments at ocean depths from 100 to 10,000 m. They can also be found in association with hydrothermal vents, methane seeps, with sunken plant material or whale carcasses.

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Anatomy

Most are less than 1 mm in diameter but 10 to 75 cm in length. They have a complex closed circulatory system and a well developed nervous system. They are the only known animals that, as adults, completely lack a mouth, gut and anus.[3] Their body is divided into four regions; the cephalic lobe, forepart, trunk, and opisthosoma. The anterior is called the cephalic lobe, which bears from 1 to over 200 thin branchial tentacles, which bears tiny side branches known as pinnules. Posterior to the cephalic lobe is the short forepart, and then the elongate trunk, which bears various annuli, papillae, and ciliary tracts. Posterior to the trunk is the short metamerically segmented opisthosoma, that contains serially arranged coelomic spaces separated by septa and bears external paired chaetae.

Vestimentiferans

Like other tube worms, vestimentiferans are marine and benthic. Riftia pachyptila, a vestimentiferan, is known only from the hydrothermal vent systems. The vestimentiferans possess an anterior first body part called the obturaculum. Their main trunk of the body bears winglike extensions, the vestimentum, from which their name is derived. Also, unlike other siboglinids that never have a digestive tract, they have one that they completely lose during metamorphosis. They feed primarily on symbiotic hydrogen sulfide- or methane-oxidizing bacteria living in an internal organ, the trophosome. One gram of trophosome tissue can contain one billion bacteria. It is not completely understood how the worms instigate their relationship with the bacteria. One theory is that the very young worm has a vent on its body permitting the entry of the bacteria from the water.[4] Their body is divided into four regions; the cephalic lobe, forepart, trunk, and opisthosoma.

The first specimen was dredged from the waters of what is now Indonesia in 1900. These specimens were given to French zoologist Maurice Caullery, who studied them for nearly 50 years.